1. Field of the Invention
The present invention relates to a semiconductor device manufacturing technology. More specifically, the present invention relates to a method for controlling a vaporizer used in an indium implantation process for implanting indium ions into a semiconductor wafer.
2. Description of the Related Art
Conventionally, a variety of ion beam technologies have been used for manufacturing integrated circuit devices. In general, ion beam technologies such as ion implantation, ion beam milling, reactive ion etching (RIE), etc., employ an ion beam from an ion source to be accelerated toward a target. The ion implantation is a standard technology for injecting dopants into a semiconductor wafer. Ion implantation is a kind of surface modification process in which ions are implanted into the near-surface region of the substrate, thereby changing the physical properties of the substrate.
Ion implantation equipment typically comprises an ion source, where ions of the desired element are produced; an accelerator, where the ions are electrostatically accelerated to a high energy; and a target chamber, where the ions impinge on a target, which is the material to be implanted. A source material is fed into the ion source in the form of a gas or solid according to its chemical and physical properties. Beam formation from a gas occurs by feeding a gas into the ion source. In the ion source, electrons, emitted from a hot filament, ionize the gas to form the plasma.
Forming a beam from a solid element (e.g., indium) can occur by a variety of methods. In one method that is commonly used in the semiconductor industry (typically demanding high-purity beams), a reactive gas, such as chlorine, is used to form the plasma. In addition, when using a solid element as source material, ion implantation equipment further comprises a vaporizer located adjacent to the ion source arc chamber. The solid element is sublimated in the vaporizer to be fed into the ion source arc chamber.
Contrary to other types of dopants, indium implantation uses a solid phase source material. Indium beams are generated using highly hygroscopic indium trichloride of which the fully hydrated form is InCl3.4H2O. Especially in indium implantation, because indium trichloride generally includes a relatively large quantity of water, the vaporizer temperature must be carefully controlled to remove water. Otherwise, when the vaporizer temperature reaches about 230° C. (e.g., under a pressure of about 1 mTorr), a hydrolysis reaction as shown in Equation 1 may occur:InCl3(c)+3/2H2O(c)→1/2In2O3(c)+3HCl(g)   [1]
Referring to Equation 1, in order to prevent formation of HCl, it is necessary to remove water before a vaporizer temperature reaches at about 230° C.
In addition, the indium trichloride source material is typically injected into the vaporizer in the form of powder. The powders may be agglomerated due to water contained in the source material. Agglomeration of powers occasionally closes an injecting tube of the vaporizer, thus interrupting the supply of the source material.